This invention relates generally to human-powered vehicles and, more particularly, to vehicles that incorporate electrical power apparatus for assisting the rider in powering the vehicle.
Vehicles of this particular kind are becoming increasingly popular, especially in urban areas, where traffic congestion and a limited availability of parking areas make the use of automobile use inconvenient and expensive. Such vehicles typically take the form of bicycles. Such bicycles are particularly popular in developing countries, where most residents are unable to afford the rather considerable cost of purchasing and maintaining automobiles.
Typically, the electrical power apparatus of such bicycles include a rechargeable battery, a dc motor that rotates a shaft engageable with a wheel of the bicycle, an electrical switch for connecting the battery to the dc motor, and a controller for controlling the switch so that the motor drives the bicycle forward in a controlled fashion. The switch typically connects the battery to the motor either directly or through a controllably variable resistor, and the controller controllably closes the switch either continuously or at a selected duty cycle.
The controller's control scheme can take many forms. For example, in many cases, control is achieved using simply a manual throttle operated by the bicycle's rider. The rider thereby can manually control the amount of electrical current delivered to the motor, and thus the torque applied by the motor to the bicycle wheel. In other cases, control is achieved by applying electrical current to the motor only after the bicycle has reached a predetermined speed. In still other cases, control is achieved by applying electrical current to the motor in proportion to the force applied by the rider to the bicycle pedals.
In all of the cases described briefly above, the controller is configured such that motor torque varies with vehicle speed in what is considered to be a non-optimum manner or such that motor torque control requires manual intervention by the rider. There is a need for an electric-assist vehicle of this kind in which the controller operates automatically, without the need for rider intervention, to connect the battery to the motor in a way that provides a torque that varies with vehicle speed according to a predetermined optimum profile. The present invention fulfills this need.